There
are two concepts of consciousness that are easy to confuse with one another,
access-consciousness and phenomenal consciousness. However, just as the
concepts of water and H2O are different concepts of the same thing,
so the two concepts of consciousness may come to the same thing in the
brain.The focus of this paper is on
the problems that arise when these two concepts of consciousness are conflated.
I will argue that John Searle’s reasoning about the function of consciousness
goes wrong because he conflates the two senses.And Francis Crick and Christof Koch fall afoul of the ambiguity
in arguing that visual area V1 is not part of the neural correlate of
consciousness. Crick and Koch’s work raises issues that suggest that these two
concepts of consciousness may have different (though overlapping)neural correlates--despite Crick and Koch’s
implicit rejection of this idea.

I will start with two quotations from Searle.You will see what appears to be a
contradiction, and I will later claim that the appearance of contradiction can
be explained if one realizes that he is using two different concepts of consciousness.I’m not going to explain yet what the two
concepts of consciousness are.That
will come later, after I’ve presented Searle’s apparent contradiction and Crick
and Koch’s surprising argument.

Searle’s Apparent
Contradiction

Searle
discusses my claim that there are two concepts of consciousness, arguing that I
have confused modes of one kind with two different kinds:

There are lots of different degrees of
consciousness, but door knobs, bits of chalk, and shingles are not conscious at
all...These points, it seems to me, are misunderstood by Block.He refers to what he calls an "access
sense of consciousness".On my
account there is no such sense.I believe
that he...[confuses] what I would call peripheral consciousness or
inattentiveness with total unconsciousness.It is true, for example, that when I am driving my car "on
automatic pilot" I am not paying much attention to the details of the road
and the traffic. But it is simply
not true that I am totally unconscious of these phenomena.If I were, there would be a car crash.We need therefore to make a distinction
between the center of my attention, the focus of my consciousness on the one
hand, and the periphery on the other..(Italics added)[1]

Note that Searle claims that if I became unconscious of the road
while driving, the car would crash.Now
compare the next argument.

...the epileptic seizure rendered the patient totally
unconscious, yet the patient continued to exhibit what would normally be
called goal-directed behavior...In all these cases, we have complex forms of apparently
goal-directed behavior without any consciousness.Now why could all behavior not be like that? Notice that in the
cases, the patients were performing types of actions that were habitual,
routine and memorized...normal, human, conscious behavior has a degree of
flexibility and creativity that is absent from the Penfield cases of the
unconscious driver and the unconscious pianist.Consciousness adds powers of discrimination and flexibility even
to memorized routine activities...one of the evolutionary advantages conferred
on us by consciousness is the much greater flexibility,sensitivity, and
creativity we derive from being conscious.[2]

Note that according to the first quotation, if I were to become
unconscious (and therefor unconscious of the road and traffic), my car would
crash.But in the second quotation, he
accepts Penfield’s description “totally unconscious” as applying to the case of
the petit mal patient who drives home while having a seizure.Thus we have what looks like a contradiction.

Crick and Koch’s Argument

I will now shift to Crick and Koch’s recent article in Nature[3]
arguing that V1(the first major processing area for visual signals) is not part
of the neural correlate of consciousness (what they call the NCC). Crick and
Koch say that V1 is not part of the neural correlate of consciousness because
V1 does not directly project to frontal cortex. (They extrapolate (tentatively)
from the fact that no direct connections are known in macaques to no
connections in humans.)Their reasoning
makes use of the premise that part of the function of visual consciousness is
to harness visual information in the service of the direct control of
reasoning and decision-making that controls behavior. On the hypothesis that
the frontal areas are involved in these mental functions, they argue that a
necessary condition of inclusion in the NCC is direct projection to frontal
areas. Though something seems right about their argument, it has nonetheless
puzzled many readers.The puzzle is
this: Why couldn’t there be conscious activity in V1 despite its lack of direct
connection to frontal cortex?This is
Pollen’s[4]worry: “I see no a priori necessity for
neurons in perceptual space to communicate directly with those in decision
space.”The possibility of conscious
activity in V1 is especially salient in the light of Crick and Koch’s
suggestion that visual consciousness is reverberatory activity in pyramidal
cells of the lower layers of the visual cortex involving connections to the
thalamus[5].
For one wonders how they have ruled out the possibility that such activity exists
in V1 despite the lack of direct connection between V1 and frontal
cortex.They do not address this
possibility at all.The overall air of
paradox is deepened by their claim that that “Our hypothesis is thus rather
subtle; if it [no direct connection] turns out to be true it [V1 is not part of
the neural correlate of consciousness] will eventually come to be regarded as
completely obvious.” (p. 123)But the
reader wonders why this is true at all, much less obviously true.When such accomplished researchers say such
puzzling things, one has to wonder if one is understanding them properly.

I will argue that once the two concepts of consciousness
are separated out, the argument turns out to be trivial on one reading and not
clearly compelling on the other reading. That’s the critical part of my comment
on Crick and Koch, but I have two positive points as well.I argue that nonetheless their conclusion
about V1 should be accepted, but for a different reason, one that they
implicitly suggest and that deserves to be opened up to public scrutiny.Further, I argue that the considerations
that they raise suggest that the two concepts of consciousness correspond to
different neural correlates despite Crick and Koch’s implicit rejection of this
idea.

The Two Concepts

The two concepts of consciousness are phenomenal consciousness
and access-consciousness[6].Phenomenal consciousness is just experience;
access consciousness is a kind of direct control.More exactly, a representation is access-conscious if it is
actively poised for direct control of reasoning, reporting and action.

One
way to see the distinction between the two concepts is to consider the
possibility of one without the other.Here is an illustration of access without phenomenal consciousness.In Anton’s Syndrome, blind patients do not
realize that they are blind (though implicit knowledge of blindness can often
be elicited).Hartmann, et. al.[7]
report a case of “Reverse Anton’s Syndrome” in which the patient does not
realize that he is not really blind.The patient regards himself as blind, and he is at chance at telling
whether a room is illuminated or dark.But he has a small preserved island of V1 which allows him to read single
words and recognize faces and facial expressions if they are presented to the
upper right part of the visual field. When asked how he knows the word or the
face, he says “it clicks” and denies that he sees the stimuli. There is no
obvious factor in his social situation that would favor lying or
self-deception.In addition to the
damage in V1, he has bilateral parietal damage, including damage to the left
inferior parietal lobe.Milner and
Goodale[8]
have proposed that phenomenal consciousness requires ventral stream activity
plus attention, and that the requisite attention can be blocked by parietal
lesions. So perhaps this is a case of visual access without visual phenomenal
consciousness.(Note that Milner and Goodale’s
account is not in conflict with Crick and Koch’s claim that V1 is not part of
the NCC if activity in V1 is not the object of attentional processes.)

So we see that access-consciousness without phenomenal
consciousness makes sense and may even exist in a limited form.What about the converse, phenomenal
consciousness without access? For an illustration at the conceptual level,
consider the familiar phenomenon in which one notices that the refrigerator has
just gone off.Sometimes one has the
feeling that one has been hearing the noise all along, but without noticing it
until it went off.One of the many
possible explanations of what happens in such a case illustrates phenomenal
consciousness without access consciousness: Before the refrigerator went off,
you had the experience (phenomenal consciousness)of the noise (let us suppose)
but there was insufficient attention directed towards it to allow direct
control of speech, reasoning or action.There might have been indirect control (the volume of your voice
increased to compensate for the noise) but not direct control of the sort that
happens when a representation is poised for free use as a premise in reasoning
and can be freely reported. (It is this free use that characterizes
access-consciousness.)On this
hypothesis, there is a period in which one has phenomenal consciousness of the
noise without access consciousness of it.Of course, there are alternative hypotheses, including more subtle ones
in which there are degrees of access and degrees of phenomenality.One might have a moderate degree of both
phenomenal consciousness of and access to the noise at first, then filters
might reset the threshold for access, putting the stimulus below the threshold
for direct control, until the refrigerator goes off and one notices the change.
The degree of phenomenal consciousness and access consciousness may always
match.Although
phenomenal-consciousness and access-consciousness differ conceptually (as do
the concepts of water and H2O), we don’t know yet whether or not
they really come to the same thing in the brain.

Once one sees the distinction, one sees many pure uses of
both concepts.For example, the
Freudian unconscious is access-unconscious.A repressed memory of torture in a red room could in principle be
a phenomenally vivid image; what makes it unconscious in the Freudian sense is
that it comes out in dreams, slips, fleeing from red rooms and the like rather
than directly controlling behavior.Thus in principle an image can be unconscious in one sense (not poised
for access), yet experienced and therefor conscious in another sense
(phenomenally).

Searle’s contradiction

Let’s go back to Searle’s (apparent) contradiction.You will recall that he says that if he were
to become unconscious of the details of the road and traffic, the car would
crash.“When
I am driving my car "on automatic pilot" I am not paying much
attention to the details of the road and the traffic.But it is simply not true that I am totally unconscious of these
phenomena.If I were, there would be a
car crash.”But he also says
that Penfield’s famous unconscious driver is “totally unconscious” yet manages
to drive home.‘(Searle has never suggested
that he changed his mind on this issue between 1990 and 1992.)Note that
there is no room for resolving the contradiction via appeal to the difference
between ‘conscious’ and ‘conscious of’.If Penfield’s driver is “totally unconscious”, then he is not conscious of
anything.And thus we have a conflict
with the idea that if one were to become unconscious of the road and traffic,
the car would crash.Can we resolve the
contradiction by supposing that what Searle thinks is that normally if
one were to become unconscious of the road the car would crash, but the
Penfield case is an abnormal exception?Not likely, since Searle’s explicit conclusion is that consciousness
adds flexibility, creativity and sensitivity to action—suggesting that he
thinks that consciousness is simply not necessary to routine activities like
driving home.

I think that appeal to the access/phenomenal distinction
does serve to resolve the contradiction.The resolution is that Searle is presupposing that the Penfield petit
mal seizure case loses phenomenal consciousness but still has sufficient
access-consciousness to drive.But when
he says that if he were unconscious of the road the car would crash, he is
thinking of loss of both phenomenal and access consciousness—and it is the loss
of the latter that would make the car crash.

I find that audiences I have talked to about this issue
tend to divide roughly evenly.Some use
‘conscious’ to mean phenomenal consciousness—to the extent that they control
their uses.Others use ‘conscious’ to
mean either access-consciousness or some kind of self-consciousness.But Searle’s error shows how easy it is for
people to mix the two concepts together, whatever their official stance is.

How Crick and Koch’s
Argument Depends on a Conflation

Crick and Koch argue that V1 is not part of the neural
correlate of consciousness because V1 does not project to frontal cortex.
Visual consciousness is used in harnessing visual information for directly
guiding reasoning and decision making and direct projection to frontal cortex
is required for such a use.But what
concept of consciousness are Crick and Koch deploying?They face a dilemma.If they mean phenomenal consciousness, then
their argument is extremely interesting but unsound: their conclusion is unjustified.If they mean access-consciousness, their
argument is trivial.Let me
explain.

Let us look at their argument more closely.Here it is:

1.Neural
machinery of visual consciousness harnessesvisual information for direct control of reasoning and decision
making

2.Frontal
areas subserve these functions

3.V1 does not project directly to
frontal cortex

4.SO V1 is not part of neural correlate of
consciousness

Note that the ‘direct’ in
premise 1 is necessary to generate the conclusion.But what reason is there to suppose that there cannot be some neural
machinery of visual consciousness—V1, for example—thatis part of the machinery of control of
reasoning and decision making, but only indirectly so?If by ‘consciousness’ we mean phenomenal
consciousness, there is no such reason, and so premise 1 is
unjustified.But suppose we take
‘consciousness’ to mean access-consciousness.Then premise 1 is trivially true.Of course the neural machinery of
access-consciousness harnesses visual information for direct control
since access consciousness just is direct control.But the trivial interpretation of premise 1
trivializes the argument.For to say
that if V1 does not project directly to areas that control action, then
V1 is not part of the neural correlate of access consciousness is to say
something that is very like the claim that if something is a sleeping
pill, then it is dormitive.Once Crick
and Koch tell us that V1 is not directly connected to centers of control,
nothing is added by saying that V1 is not part of the neural correlate of
consciousness in the access sense. For an access-conscious
representation just is one that is poised for the direct control of
reasoning and decision making.

On
this reading, we can understand Crick and Koch’s remark about their thesis that
“if it [V1 is not directly connected to centers of control] turns out to be
true it [V1 is not part of the neural correlate of consciousness] will
eventually come to be regarded as completely obvious.”On the access-consciousness interpretation,
this remark is like saying that if it turns out to be true that barbiturates
cause sleep, their dormitivity will eventually come to be regarded as
completely obvious.

To avoid misunderstanding, I must emphasize that I am not
saying that it is a triviality that neurons in V1 are not directly connected to
frontal areas.That is an empirical
claim, just as it is an empirical claim that barbituates cause sleep.What is trivial is that if neurons in V1 are
not directly connected to centers of control, then neurons in V1 are not part
of the neural correlate of access-consciousness.Similarly, it is trivial that if barbituates cause sleep, then
they are dormitive.

That was the “access-consciousness” interpretation.Now let us turn to the phenomenal
interpretation.On this interpretation,
their claim is very significant, but not obviously true?How do we know whether activity in V1 is
phenomenally conscious without being access-conscious? As mentioned earlier,
Crick and Koch’s own hypothesis that phenomenal consciousness is reverberatory
activity in the lower cortical layers makes this a real possibility.They
can hardly rule out this consequence of their own view by fiat.Crick and Koch[9]
say, “We know of no case in which a person has lost the whole prefrontal and
premotor cortex, on both sides (including Broca’s area), and can still see.”
But there are two concepts of seeing, just as there are two concepts of
consciousness.If it is the phenomenal
aspect of seeing that they are talking about, they are ignoring the real
possibility that patients who have lost these frontal areas can see.

Crick and Koch attempt to justify the ‘directly’ by
appeal to representations on the retina.These representations control but not directly; and they are not
conscious either.Apparently, the idea
is that if representations don’t control directly, then they are not conscious.But this example cuts no ice.Retinal representations have neither
phenomenal nor access-consciousness.So they do not address the issue of whether V1 representations might
have phenomenal but not access-consciousness.

So Crick and Koch face a dilemma: their argument is
either not substantive or not compelling.

Is the Point Verbal?

Crick and Koch often seem to have phenomenal
consciousness in mind. For example, they orient themselves towards the problem
of “a full accounting of the manner in which subjective experience arises from
these cerebral processes...Why do we experience anything at all? What leads to
a particular conscious experience (such as the blueness of blue)? Why are some
aspects of subjective experience impossible to convey to other people (in other
words, why are they private)?”[10]

Crick
and Koch often use ‘aware’and ‘conscious’ as synonyms, as does Crick in The
Astonishing Hypothesis.For
example, the thesis of the paper in Nature1is that V1
is not part of the neural correlate of consciousness and also that V1 is not
part of the neural correlate of visual awareness.But sometimes they appear to use ‘awareness’ to mean access-consciousness.
For example, “All we need to postulate is that, unless a visual area has a
direct projection to at least one of [the frontal areas], the activities in
that particular visual area will not enter visual awareness directly,
because the activity of frontal areas is needed to allow a person to report consciousness” (p 122,
emphases added).What could
‘consciousness’ mean here?‘Consciousness’ can’t mean access consciousness, since reporting
is a kind of accessing, and there is no issue of accessing access-consciousness.
Consciousness in the sense in which they mean it here is something that might conceivably
exist even if it cannot be reported or otherwise accessed.And consciousness in this sense might exist
in V1. Thus when they implicitly acknowledge an access/phenomenal consciousness
distinction, the possibility of phenomenal without access consciousness looms
large.

My point is not a verbal one.Whether we use ‘consciousness’or ‘phenomenal consciousness’,
‘awareness’ or ‘access-consciousness’, the point is that there are two
different concepts of the phenomenon or phenomena of interest.We have to acknowledge the possiblity in
principle that these two concepts pick out different phenomena. Two vs. one:
that is not a verbal issue.

Are the Neural Correlates of the Two Kinds of Consciousness Different?

Perhaps there is evidence that the neural correlate of
phenomenal consciousness is exactly the same as the neural correlate of
access-consciousness?The idea that
this is a conceptual difference without a real difference would make sense both
of Crick and Koch as well as other work in the field. But paradoxically, the
idea that the neural correlates of the two concepts of consciousness coincide
is one which Crick and Koch themselves actually give us reason to reject.Their hypothesis about the neural correlate
of visual phenomenal consciousness is that it is localized in
reverberatory circuits involving the thalamus and the lower layers of the
visual cortex3.This is a
daring and controversial hypothesis.But it entails a much less daring and controversial conclusion: that the
localization of visual phenomenal consciousness does not involve the frontal
cortex.However, Crick and Koch
think that the neural correlate of consciousness—and here we would be
charitable in interpreting them as meaning access-consciousness--does
involve the frontal cortex.It would
not be surprising if the brain areas involved in visual control of reasoning
and reporting are not exactly the same as those involved in visual
phenomenality.

One way for Crick and Koch to respond would be to include
the neural correlates of both access and phenomenal consciousness in the
“NCC”.To see what is wrong with this,
consider an analogy.The first
sustained empirical investigation of heat phenomena was conducted by the
Florentine Experimenters in the 17th Century.They didn’t distinguish between temperature
and heat, using a single word, roughly translatable as “degree of heat”, for
both.This failure to make the
distinction generated paradoxes.For
example, when they measured degree of heat by the test “Will it melt paraffin?”
heat source A came out hotter than B, but when they measured degree of heat by
how much ice a heat source could melt in a given time, B came out hotter than A[11].The concept of degree of heat was a mongrel
concept, one that lumps together things that are very different4.

The suggestion that the neural correlate of visual
consciousness includes both the frontal lobes and the circuits involving
the thalamus and the lower layers of the visual cortex would be like an advocate
of the Florentine Experimenters’ concept of degree of heat saying that the
molecular correlate of degree of heat includes both mean molecular
kinetic energy (temperature) and total molecular kinetic energy (heat),
an idea that makes little sense.The right
way to react to the discovery that a concept is a mongrel, is to
distinguish distinct tracks of scientific investigation corresponding to the
distinct concepts, not to lump them together.

Another way for Crick and Koch to react would be to
include both the frontal lobes and the circuits involving the thalamus and the
lower layers of the visual cortex in the neural correlate of phenomenal
consciousness.(Koch seems inclined in
this direction in correspondence.)But
this would be like saying that the molecular correlate of heat includes
both mean and total molecular kinetic energy.Again, this makes little sense.The criteria that Crick and Koch apply in localizing visual phenomenal
consciousness are very fine grained, allowing them to emphasize cortical layers
4, 5 and 6 in the visual areas. For example, they appeal to a difference in
those layers between cats which are awake and cats which are in slow wave
sleep, both exposed to the same visual stimuli. No doubt there are many
differences between the sleeping and the waking cats in areas outside the
visual cortex.But we would need a very
good reason to include any of those other differences in the neural correlate
of visual phenomenology as opposed, say, to the non-phenomenal cognitive
processing of visual information.

A Better Reason for not Including V1 in the NCC

Though I find fault with one strand of Crick and Koch’s
reasoning about V1, I think there is another strand in the paper that does
justify the conclusion, but for a reason that it would be good to have out in
the open and to distinguish from the reasoning just discussed.(Koch tells me that what I say in this
paragraph is close to what they had in mind.)They note that it is thought that representations in V1 do not exhibit
the Land effect (color constancy).But
our experience, our phenomenal consciousness, does exhibit the Land effect, or
so we would all judge.Similarly, it
appears that neurons in V1 are sensitive to gratings that are finer than people
judge they can make out.We should
accept the methodological principle: at this early stage of inquiry,
don’t suppose that people are wildly wrong about their own experience.Following this principle and assuming that
the claim that cells in V1 don’t exhibit color constancy is confirmed, then we
should accept for the moment that representations in V1 are not on the whole
phenomenally conscious. This methodological principle is implicitly accepted
throughout Crick’s and Koch’s work.

An
alternative route to the same conclusion would be the assumption that the
neural correlate of phenomenal consciousness is “part of” the neural correlate
of access-consciousness (and so there can be no phenomenal without
access-consciousness).Phenomenal
consciousness is automatically “broadcasted” in the brain, but perhaps there
are other mechanisms of broadcasting.So even if the “reverse Anton’s syndrome” case turns out to be access
without phenomenal consciousness, Crick and Koch’s conclusion might still stand.

Note
that neither of the reasons given here make any use of the finding that V1 is
not directly connected to frontal areas.

The assumption that phenomenal consciousness is part of
access consciousness is very empirically risky.One empirical phenomenon that favors taking phenomenal without
access conscious seriously is the fact that phenomenal consciousness has a
finer grain than access-consciousness based on memory representations.For example, normal people can recognize no
more than 80 distinct pitches, but it appears that the number of distinct
pitch-experiences is much greater.This
is indicated (but not proven) by the fact that normal people can discriminate
1400 different frequencies from one another[12].
There are many more phenomenal experiences than there are concepts of them.

Despite these disagreements, I greatly admire Crick’s and
Koch’s work on consciousness and have written a very positive review of Crick’s
book.[13]
Crick has written “No longer need one spend time ...[enduring] the tedium of
philosophers perpetually disagreeing with each other.Consciousness is now largely a scientific problem.”[14]
I think this conceptual issue shows that even if largely a scientific issue, it
is not entirely one.There is still
some value in a collaboration between philosophers and scientists on this
topic.[15]

[15]This is a substantially revised version of a paper
that appeared in Trends in Neuroscience,19, 21996.I am grateful to
audiences at the 1996 consciousness conference in Tucson, at the 1996 cognitive
science conference at the University of Sienna, at the University of Oxford,
Department of Experimental Psychology, at Union College Department of
Philosophy and the Royal Institute of Philosophy.I am also grateful to Susan Carey, Francis Crick, Martin Davies,
Christof Koch, David Milner and to the editor of Trends in Neuroscience for comments on a previous draft.